1. Field of the Invention
This invention concerns the decoration of metal surfaces of complex configuration. More particularly, this invention relates to transfer printing of metal objects of complex configuration.
2. Background Art
Transfer printing of inks or dyes into a variety of articles such as shirts, mugs, plastic articles and plastic coated substrates is well-known in the art. Dispersible dye crystals or inks are printed in reverse images in transfer paper which is to be used to transfer print the article to be decorated. The article to be decorated is usually made of plastic or has a plastic or polymer coating on it into which the dyes are transferred.
Most transfer printing is referred to as sublimation printing in which the dyes are said to sublimate under heat and pressure to be driven into any receptive substrate that is put in contact with the transfer paper. Such sublimation printing was developed circa 1969 and has been used extensively to print many articles including plastic coated metal substrates.
Transfer printing also includes a melt printing process which is as described in several patents and patent applications including U.S. Pat. Nos. 4,587,155; 4,670,084; 4,668,239 and Published Application WO 92/21514. According to U.S. Pat. No. 4,587,155, the desired dye image is transferred from the paper to the substrate by heating the dye to a temperature above its melting point but below its vaporization temperature so that the dye will diffuse into the softened plastic substrate. Published Application WO 92/21514 describes melt printing of planar metal base members such as aluminum, steel or the like which have been coated on at least one planar surface with a melt printable layer of softenable, dye-permeable, thermoplastic or thermoset material such as polyethylene terephthalate, polybutylene terephthalate or other thermoplastic polyesters, polycarbonates, nylons and the like. Application WO 92/21514 further describes bilayer coatings of thermoplastic or thermoset materials including a base coat optimally provided with a pigment and a second layer that can comprise a clear resin. The application states that neither the composition nor the thickness of either the substrate or the printable plastic layers is critical.
Canadian Patent 1,108,929 describes a process for applying designs to unsealed, anodized aluminum which is continuously heated to a temperature at which colored components of ink will sublime. The heated strip is fed into contact with an ink carrying web so the ink is heated and transferred into the anodized aluminum surface. The decorated aluminum strip is then cooled with water and passed through a sealing bath filled with a sealing solution such as buffered aqueous nickel.
Unfortunately, none of these references provide any insight into how to produce a high-quality image on a metal object of complex configuration such as a metal sphere or a tapered cylinder. An improved process is needed for transfer printing metal objects of complex shape in order to produce objects having consistent bright coloring with little or no texturing of the surface of the object.